Biostimulants Based on Humic Acids, Amino Acids and Vitamins Increase Growth and Quality of Lettuce Seedlings

Humic acids (HA), amino acids (AA) and vitamins can increase plant growth; however, there are still few studies that determine the ideal concentration for use in lettuce (Lactuca sativa L.) production. Research was conducted to evaluate the effects of HA enriched with sources and levels of AA and vitamins on lettuce seedlings morphology and quality. Two experiments were conducted in a completely randomized design with four replicates. The first experiment had 16 treatments, 3 × 5 + 1 factorial design, the first factor was betaine, glycine and proline used in the HA enrichment, and second factor five concentrations of AA (0, 0.5, 1.0, 1.5, and 2.0 g L-1), plus the control, without HA and AA. The second experiment had 21 treatments, 4 × 5 + 1 factorial design, the first factor was the use of four vitamins (A, E, B1 and B2) in the enrichment of HA, while the second factor was composed of five concentrations of each vitamin (0, 0.5; 1.0, 1.5, and 2.0 g L-1) plus the control, without HA and vitamins. The application of HA and HA+AA promote the improvement in the seedling’s morphology and quality, while the application of the HA+vitamins negatively affected the morphology, reducing seedling quality.